Variable-voltage transformer.



No. 865,985. PATENTED SEPT. 17, 1907. T. M. BAINS, Jn.

VARIABLE VOLTAGE TRANSPORMER.

" APPLIoATIox FILED 223.13.1907.

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Inventor;

0V Thomas Mai Jr: y Oqtty UNITED- STATES l1 rrrriivi onnron.

THOMAS M. BAINS, JR., OF PHILADELPHIA, PENNSYLVANIA, ASSIGNORl TOGENERAL ELEOTRICCOMPANY, A CORPORATION OF NEW YORK.

VARIABLE-VOLTAGE TRANSFORMER.

Specification of Letters Patent.

Patented Sept. 17, 1907.

Application filed February 8, 1907. Serial No. 356,478.

To all whom 'it may concern:

Be it known that I, THoMAs M. BAINS, Jr., a citizen of the UnitedStates, residing at Philadelphia, county of Philadelphia, State ofPennsylvania, have invented certain new and useful Improvements inVariable-VoL tage Transformers, of which the following is aspecification.

My invention relates to variable-voltage transformers oi the type inwhich the primary flux is shifted into and out of inductive relation tothe secondary'winding, so as to vary the induced'secondary voltage.

The object of my invention is to provide a novel construction for, suchtransformers, which is compact and of high efiiciency.

In carrying out my invention, I arrange the core with three legs andmount the primary coil on one leg with the secondary coil surroundingboth the leg on which, the primary coil is placed, and also a secondleg. And I provide a movable. magnetic member for shifting the primaryflux from one to the other of the other two legs.

Or, expressed in another way, I arrange the secondary coil outside oftheprimary coil with an inside diameter substantially greater than theouter diameter of the primary coil, and shift the primary-flux from areturn-path within the secondary coil to' a return -path outside of it.When the flux returns through the secondary coil, it induces no voltagein it, but when it returns outside the secondary coil, the primary fluxis interlinked with the secondary coilin the usual manner.

My invention further comprises employing an auxiliary secondary coil, soarranged as to oppose the induced secondary voltage, due to leakage, inthe position of minimum voltage, so as to securea resultant secondaryvoltage of aero. This coil is so arranged as to be of practically noeffect when the induced secondary voltage is at'its maximum. 'Y

My invention will best be understood byl reference to the accompanyingdrawings, in which v Figure l shows a side elevation in cross-section ofa variable voltage transformer arranged in accordance withniy invention;Fig. 2 shows a. plan view of the same; Fig. 3 shows the core andcoilsdiagrammatically; and Fig. 4 shows a modification.

In the drawings, A represents d magnetic core, which has three parallellegs al, a2, and a, On thel central leg a2 is mounted the primary coilB.

(l is thesecondary coil, which surrounds' both the primary coil `B andthe lleg h1. The secondary coil thus has an inside diametersubstantially greater than the outer diameter of the primary coili-Drepresents a movable magnetic member which is supported from and slideson the' rods E; being moved nearly closed magnetic circuit with the legsa1 and a2, so that the primary flux in the leg a2 finds a return paththrough the leg a1. This return path is inside the secondary coil,and-induces no voltage in the secondary coil, so that this position ofthe member D corresponds to minimum secondary voltage. When the member Dis moved into the position shown in dotted lines in Fig. 3, a nearlyclosed magnetic circuit is formed with the legs a2 and a3. The primaryflux now returns outside the secondary coil (l, and is consequentlylinked with this coil in thc usual manner. The dotted line position ofmember D is consequently the position oi maximum induced secondaryvoltage. At intermediate positions the induced voltage will haveintermediate value.

If it were not for leakage, the induced secondary voltage would be zero,with the arrangement of windings shown in Fig. 3. when the member D isin its full-line position. A certain portieri of the primary flux,however, will leak across .to the leg ai. and consequently returnoutside of the secondary coil. This leakage iiux is interlinked with thesecondary coil and induces a certain voltage therein. In order that theminimum value of the secondary voltage may be zero, l make useof theauxiliary secondary winding c, shown in Fig. 4. I place this winding onthe leg a1 and connect it in opposition to the main secondary winding C.When the vmember D is in the position oi minimum induced secondaryvoltage, which is the dotted-line position in Fig. 4, the greater partof the primary flux is linked with the auxiliary Winding c and inducestherein a voltage which neutralizes the voltage induced in the mainsecondary winding C by the leakage flux, so that the resultant secondaryvoltage is zero. When the member D is in the full-line position in Fig.4, in which the indliced secondary voltage is maximum, the auxiliarysecondary winding c is threaded only by a small leakage flux, andconsequently has a practically negligible effect.

` l I do not desire to limit myself to the particular construction andarrangement of parts here shown, but aim in the appended claims to coverall modifications' which are within the scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,-

1. In a variable voltage transformer, a three-legged core, a primarywinding surrounding one leg, a secondary winding surrounding both theleg carrying the primary winding and a second leg, and means fordirecting the iiux from the leg carrying the primary winding through theotherv two legs alternately.

2. In a variable voltage transformer, a three-legged core, a primarywinding sux-rounding one leg, a secondary winding surrounding both theleg carrying the primary winding and a second leg, und meansforgradually shifting the return ilux of the primary winding from oneto' the other vo1! the other two legs.

3. In a variable voltage transformer, a three-legged 'leg carrying theprimary winding' and either of the other legs.

4. in a variable voltage transformer, a primary coil, a secondary collsurrounding the primary and having an inside diametersubstantiallygreater than the outside diameter of the primary coil, and means forcausing;r the flux passing through the primary coil to return eitherinside or outside the secondary coil.

5. In a variable voltage transformer, a primary coil, a secondary coilsurrounding the primary and having an inside diameter-substautiallygreater than the outside diameter of the primary coil, and a movablemagnetic member adapted `aradually to shift the flux passing through theprimary coil from a return path inside the secondary coil to a returnpath outside it.

(i. ln a variable voltage transformer, a three-legged core, a primaryWinding.: surrounding one leg. u main secondary winding surrounding both the leg carrying the adapted gradually to shift the tiux passingthrough the v primary coil from a return path inside'the main secondarycoil lto a return path outside it, and an auxiliary secondary coil inlinductive relation to the return path within the mainsecondary coil andconnected in opposition to the main secondary coil. V

in witness whereof, I have hereunto set my hand this 25th day ofJanuary, 1907. 'rrioMAs M. BAINS, .nu

Witnesses: 4

L. T. MmrwiN, BEN Nonni.

